Uterine responses and equine chorionic gonadotropin concentrations after two intrauterine infusions with kerosene post early fetal loss in mares

Pregnancy loss during the normal lifespan of endometrial cups (∼37-120-150 days of gestation) may affect a mare's ability to conceive again in the same breeding season, as equine chorionic gonadotropin (eCG) secretion by retained endometrial cups can lead to abnormal ovulations and follicular growth. While intrauterine kerosene infusion has anecdotally been proposed as a treatment for endometrial cup retention, there are no controlled studies evaluating kerosene's ability to enhance endometrial cup regression following abortion. The objectives of this study were to assess uterine response, systemic side effects, and efficacy of intrauterine kerosene infusions after abortion. We hypothesized that kerosene infusions would hasten regression of endometrial cups without detrimental effects on the endometrium and the mare's general health. Twelve light-breed mares were enrolled in the study after an experimentally induced abortion with cloprostenol (n = 12) by 60 ± 2 days of gestation. Mares were randomly allocated to receive an intrauterine infusion with 500 mL of kerosene (n = 6) or 500 mL saline (n = 6) on days 21 and 35 after pregnancy termination. Uterine biopsies were collected at days 7, 21, 35, and 49 post-abortion to evaluate the degree of endometrial fibrosis with Picrosirius Red Stain and to be graded according to the Kenney & Doig 1986 classification. Furthermore, histomorphometry analysis of the endometrium lining, glandular epithelium and glandular density was performed. Endometrial lymphocyte B CD20⁺, lymphocyte T CD3⁺, and macrophage IBA-1⁺ cell populations were characterized by immunohistochemistry. Physical examinations, blood cell counts, and serum biochemistry were performed before, and for 2 days after each uterine infusion. Serum samples were collected for assessment of eCG concentrations. Continuous data were analyzed with MIXED procedure with repeated measures in SAS, categorical data with LOGISTIC procedure of SAS. Significance was set at p < 0.05. Kerosene infusion did not affect complete blood cell counts, serum chemistry parameters, or physical examinations. Concentrations of eCG decreased over time (p < 0.001), but there were no differences between groups or time by group interactions (p = 0.72). Histological evaluation of the uterus showed no signs of increased fibrosis or degeneration in the treatment group. In conclusion, while kerosene infusions did not appear to have detrimental effects on mare health, our findings suggest that the use of kerosene in the uterus does not enhance the regression of endometrial cups by 49 days post-abortion.